Manufacturers of nonroad diesel power systems are expected to meet set emissions regulations. For example, Tier 3 emissions regulations required an approximate 65 percent reduction in particulate matter (“PM”) and a 60 percent reduction in nitrogen oxides (“NOx”) from 1996 levels. As a further example, Interim Tier 4 regulations required a 90 percent reduction in PM along with a 50 percent drop in NOx. Still further, Final Tier 4 regulations, which will be fully implemented by 2015, will take PM and NOx emissions to near-zero levels. Manufacturers of maritime power systems are also expected to meet emissions regulations, though they vary from the nonroad emissions regulations (e.g., International Maritime Organization regulations).
One technique for reducing NOx involves introducing chemically inert gas into the fresh intake gas for subsequent combustion. By reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures lower, which lowers NOx production. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gas, and one known method for achieving the foregoing result is through the use of an EGR system operable to controllably introduce a recirculated portion of the exhaust gas, from the exhaust manifold, into an intake manifold. Having an EGR system results in cooler combustion temperatures, reduced NOx formation, optimized fuel economy, and improved overall performance.
Modern power systems often times have one or more turbochargers, which are an effective means for supplying increased fresh intake gas volume and pressure. However, at low engine speeds and simultaneous high engine loads, some turbochargers may be prone to providing insufficient boost, resulting in the formation of engine smoke.